1. Field of the Invention
The invention relates to a device and a process for liquid treatment of a surface of a wafer-shaped article.
2. Description of Related Art
Liquid treatment includes both wet etching and wet cleaning, wherein the surface area of a wafer to be treated is wetted with a treatment liquid and a layer of the wafer is thereby removed or impurities are thereby carried off. A device for liquid treatment is described in U.S. Pat. No. 4,903,717. In this device the wafer-shaped article is mounted on a spin chuck and treatment liquid is applied from above the chuck onto the surface of the wafer not facing the chuck. The distribution of the liquid may be assisted by the rotational motion of the wafer. Such rotational motion may also assist in removing the liquid from the surface of the wafer as the liquid is flung off laterally over the edge of the wafer. The '717 patent discloses a chuck that flushes the chuck-facing surface of the wafer with a gas. In doing so, an annular nozzle is formed between the peripheral edge of the chuck and the peripheral edge of the main surface of the wafer facing the chuck. The flowing gas is exhausted from this annular nozzle and thereby limits the extent to which treatment liquid can flow onto the chuck-facing surface of the wafer; however, there is no provision for limiting treatment of the edge surfaces of the wafer while treating the upper main surface of the wafer.
U.S. Pat. No. 6,328,846 discloses guide elements on the periphery of a spin chuck that selectively engage the edge of a wafer supported by the chuck and thereby limit undesirable lateral motion of a wafer while it is being treated. Three or more pins in the shape of cylinders are disclosed as sufficient to limit the lateral motion of the wafer when spaced around the wafer and moved to engage the wafer's edge. The pins are disposed perpendicular to the main surface of the wafer and the chuck and extend above the chuck through bores. The pins extend above the edge of the wafer and move against the wafer after placement on the chuck. In the embodiment disclosed in the patent, the wafer floats above the chuck on a cushion of gas exhausted from the chuck. The gas flushes the surface of the wafer facing the chuck and is exhausted from the chuck at the peripheral edge of the wafer.
The '846 patent discloses that treatment liquid can flow along the pins when engaged against the wafer's edge and treat the lower opposite main surface of the wafer, leading to so called pin marks on the wafer's edge and chuck-facing surface. To avoid this problem, the '846 patent discloses a separate nozzle associated with each pin and localized at the pin structure to flush the pin area with a gas. The gas prevents the treatment liquid from flowing along the pin and treating the edge surfaces and chuck-facing surface of the wafer.